The present invention relates to a novel catalyst system using a novel solid catalyst component for the polymerization of .alpha.-olefins and a process for producing .alpha.-olefin polymers using such catalyst system.
Catalyst systems comprising titanium trichloride and an organoaluminum compound have hitherto been used for the industrial production of high crystalline polymers of .alpha.-olefins such as propylene, butene-1, etc. Since the polymerization proceeds in such a state that a solid titanium trichloride is embraced by the formed polymer, the titanium trichloride partly remains in the product polymer. This residue causes adverse effects on the color, heat stability, and other properties of the polymer. Hence, an extraction step was generally necessary to remove the residue from the polymer. On the other hand, an amorphous polymer called "atactic polymer" is incidentally produced in the polymerization. When remaining in the product polymer, said atactic polymer deteriorates mechanical properties of molded products of the polymer and may give stickiness thereto. This required generally a washing step for removing the atactic polymer from the objective polymer.
These additional operations resulted in economical disadvantages with respect to materials and energy, so that a simplified process was intensively desired. Up to now, various improvements have been made in the preparation of titanium trichloride. As a result, the polymerization activity and/or stereospecificity of the catalyst were greatly improved and this enabled the industrialization of polymerization processes simplified with respect to the above-said operations. The present inventors disclosed formerly such an improved process for preparation of titanium trichloride in Japanese Patent Publication No. 27085/80 and subsequently a further improvement of this process in Japanese Patent Application Kokai (Laid-Open) No. 116706/81. However, when the solid product obtained by reducing titanium tetrachloride with an organoaluminum compound or the heat-treated material of said solid product was used as a titanium trichloride composition as described in the above patents, parts of these titanium trichloride composition particles were disintegrated into fine particles during the activation treatment of the composition with a halogen compound-ether compound mixture or with a halogen compound-ether compound-electron donative compound mixture, resulting in a great difficulty of filtration in the washing of the activated composition. This obliged the use of the decantation method, which was inferior in the effect of solid-liquid separation. Additionally, on drying the washed composition, a great number of stiff agglomerates were produced therefrom. When said titanium trichloride composition was used as such for the polymerization of olefin, there were fears of clogging of the solid-catalyst feed line was such agglomerates and of the polymer discharge valve with polymer blocks formed in the polymerization reactor. It was therefore necessary to remove the agglomerates by sieving or the like.
There have been proposed some methods in order to prevent the disintegration of titanium trichloride particles during the activation treatment. The proposed methods comprise polymerizing a small amount of .alpha.-olefins on a .beta.-titanium trichloride-containing solid product obtained by reducing titanium tetrachloride with an organoaluminum compound, prior to the activation treatment of this solid product (Japanese Patent Application Kokai (Laid-Open) Nos. 58206/80, 145117/81, and 5314/83). According to these methods, the disintegration of titanium trichloride particles is surely prevented, but coarse particles of the catalyst are formed by agglomeration particularly when propylene is preliminarily polymerized on the catalyst or when the activation treatment is conducted in an aromatic hydrocarbon solvent.
As a result of intensive studies, the present inventors found a novel catalyst system using a novel solid catalyst component for .alpha.-olefin polymerization, which is highly active, highly stereospecific, and good in particle character. Said solid catalyst component is prepared by the reduction of titanium tetrachloride with an organoaluminum compound, heat treatment of the reduction product, preliminary polymerization of .alpha.-olefin to treat the thus obtained solid product containing .gamma.-titanium trichloride, and activation treatment of the preliminary polymerization treated product with a halogen and/or an interhalogen compound and with an ether compound. Based on this finding, this invention has been accomplished.